Control valves
Safety valves
4.7.39
Total steam
temperature
°F
280
300
320
340
360
380
400
420
440
460
Set pressure psi g
15
20
40
60
80
100 120 140 160 180 200 220 240 260 280 300
Saturated steam temperature °F
250
259 287 308
324 338 350 361 371 380 388 395 403 409 416 422
1.00 1.00
1.00 1.00
1.00 1.00
0.99 0.99
0.99 0.99
-
-
-
-
1.00
-
-
-
1.00 1.00
1.00 1.00
0.99 0.99
-
-
1.00
-
1.00 1.00
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.00
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.98 0.98
0.98 0.98
0.97 0.97
0.96 0.96
0.95 0.95
0.99 0.99
0.98 0.98
0.97 0.97
0.96 0.96
0.95 0.95
0.99 1.00
0.99 0.99
0.98 0.98
0.97 0.97
0.96 0.96
1.00 1.00 1.00
0.99 1.00 1.00
0.98 0.99 0.99
0.97 0.98 0.98
0.96 0.96 0.97
-
-
1.00 1.00
0.99 0.99
0.98 0.99
0.97 0.97
-
-
-
-
-
1.00
-
-
-
-
1.00 1.00 1.00 1.00
-
0.99 0.99 0.99 1.00 1.00
0.98 0.98 0.98 0.99 0.99
Safety valve sizing information
Formulas:
For steam service:
For organic fluid vaporizers - lb / h:
Where:
A =
P =
T =
s
=
K
d
=
K
sh
=
M =
C =
Z =
Required orifice area in square inches
Relieving pressure in pounds per square inch absolute = set pressure (psi g) + overpressure + 14.7 where the overpressure is
3% or 2 psi, whichever is the greater. P = 1.03 x set pressure + 14.7 or P = set pressure + 2 psi + 14.7.
Inlet temperature, °F. Absolute (°F plus 460).
Required steam capacity in pounds per hour.
= Required vapor capacity in pounds per hour.
Coefficient of discharge, 0.955 for steam, air and vapour service.
Steam superheat correction factor. See Table 1 below.
Average molecular weight of vapour. See Table 3, page 5.
Gas or vapour flow constant. See Table 2, page 5.
Compressibility factor corresponding to T and P. If this factor is not available, compressibility correction can be safely ignored using
a value of Z = 1.0.
Table 1 K
sh
superheat correction factor
Do not exceed the maximum operating temperature of 446°F.
TI-S13-30 CH Issue 13
SV74 Carbon Steel Safety Valve
Page 4 of 5
